Brook (stream)
A brook is a small natural stream or watercourse, sometimes also referred to as a rivulet. It is typically shallow and carries less water than larger streams and rivers. The term is sometimes used particularly for a stream that originates from a spring or seep. The distinction between a brook and other small watercourses, particularly a creek, is not precisely defined. The names given to flowing watercourses vary according to regional usage, historical naming conventions and local geography, and there is no universally accepted width, depth or discharge at which a brook becomes a creek or river. Particularly small brooks may also be known as rills or streamlets.
Read on Wikipedia